JP2008047206A - Optical pickup and optical disk device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup detecting servo signals corresponding to different three wavelengths and achieving an optical component reduced in size, a device reduced in size, and cost reduction. <P>SOLUTION: The optical pickup includes a first exit part 31 for a first wavelength, a second exit part 32 for a second wavelength longer than the first wavelength, a third exit part 33 for a third wavelength longer than the second wavelength, objective lenses 34, 35, a photodetector 36 detecting return light, and a polarization diffraction element 50 in which a first diffraction area diffracting the return light to a prescribed direction and a second diffraction area diffracting a light beam transmitting therethrough to another prescribed direction are alternately formed. A focus error signal is detected on the basis of a light quantity of the light beam received by respective light reception parts receiving the light beams diffracted by the first and second diffraction areas. In the first and second diffraction areas, diffraction efficiency of secondary diffracted light of the light beam having the first wavelength are ≥70%, and the diffraction efficiency of the primary diffracted light of the light beams having the second and third wavelengths are ≥70%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup used for recording an information signal on an optical disc and reproducing the information signal recorded on the optical disc, and an optical disc apparatus using the optical pickup.

  Conventionally, optical signals such as CDs (Compact Discs) and DVDs (Digital Versatile Discs) have been used as information signal recording media, and light beams having a wavelength of about 405 nm using a blue-violet semiconductor laser or the like to enable higher density recording. An optical disc for recording and reproducing signals (hereinafter referred to as “high-density recording optical disc”) is used, and an optical signal is recorded to record an information signal on this type of optical disc or to reproduce an information signal recorded on the optical disc. A pickup is used.

  In such an optical pickup, it is necessary to perform focus control and tracking control in order to focus a light beam spot on a predetermined track of an optical disk by an objective lens. In order to detect a focus error signal for focus control, an astigmatism method, a spot size method, a Foucault method, and the like have been proposed. Here, the astigmatism method has a problem that a tracking error signal leaks into the focus error signal when the position of the spot on the light receiving element is shifted. In the Foucault method, the spot on the light receiving element is small, and the tolerance for the positional deviation of the light receiving element is small and there is a problem in reliability.

  On the other hand, in the spot size method, since the diffraction angle is proportional to the wavelength of a prism or a diffraction element, the light is received by a high-density recording optical disk having a relatively short use wavelength and a conventional optical disk such as a CD having a relatively long use wavelength. In order to make the pattern common, there is a problem that the size of the light receiving element becomes too large, and the wavelength dependence of the diffraction efficiency is large. With the conventional step type diffraction element, the performance for all wavelengths corresponding to the formats of a plurality of optical disks ( There is a problem that it is difficult to establish (diffraction efficiency).

JP 2002-260251 A

  An object of the present invention is to provide an optical pickup capable of satisfactorily detecting a focus error signal corresponding to three different wavelengths and realizing miniaturization of an optical component, miniaturization of an apparatus, and cost reduction, and an optical disc using the same. To provide an apparatus.

  In order to achieve this object, an optical pickup according to the present invention includes a first emitting unit that emits a light beam having a first wavelength, and a light beam having a second wavelength that is longer than the first wavelength. A second emission part that emits light, a third emission part that emits a light beam having a third wavelength longer than the second wavelength, and first and third emission parts emitted from the first to third emission parts. An objective lens for condensing the light beam having the first to third wavelengths on the signal recording surface of the optical disc, a photodetector for detecting the return light beam reflected by the signal recording surface of the optical disc, and the first to first components. 3 and the objective lens, and separates the optical path of the return light beam from the optical path of the light beam emitted from the first to third exit parts, thereby returning the return light. Optical path separating means for guiding the beam to the photodetector side, the photodetector, A first diffractive region provided between the optical path separating means and diffracting the passing light beam in a predetermined one direction and a second diffractive region diffracting the passing light beam in a predetermined other direction alternately A polarization diffraction element formed, and the photodetector includes a first light receiving unit that receives a light beam diffracted in the first diffraction region, and a light beam diffracted in the second diffraction region. The light beam diffracted in the first diffraction region is condensed on the front side of the first light reception unit, and is diffracted in the second diffraction region. The light beam is condensed on the rear side of the second light receiving unit, and a focus error signal is detected based on the light amount of the light beam received by the first and second light receiving units. When the incident light beam has a predetermined polarization direction, the light beam is diffracted, When the emitted light beam has a polarization direction orthogonal to the predetermined polarization direction, the light beam is transmitted, and the first and second diffraction regions are light quantities of the light beam in the polarization state to be diffracted. In contrast, the diffraction efficiency of the second-order diffracted light of the light beam of the first wavelength is 70% or more, and the diffraction efficiency of the first-order diffracted light of the light beams of the second and third wavelengths is 70% or more. .

  In order to achieve the above-described object, an optical disc apparatus according to the present invention is an optical disc apparatus including an optical pickup that records and / or reproduces information with respect to an optical disc, and a disc rotation driving unit that rotates the optical disc. As the optical pickup used in this optical disc apparatus, the one described above is used.

  The optical pickup according to the present invention and the optical disc apparatus using the same can detect a focus error signal corresponding to three different wavelengths well, and realize downsizing of optical parts, downsizing of the apparatus, and cost reduction. To do.

  Hereinafter, an optical disk apparatus to which the present invention is applied will be described with reference to the drawings.

  This optical disk apparatus 10 is an optical disk apparatus capable of recording and / or reproducing information signals with respect to two types of optical disks 11 having different formats.

  The optical disk 11 used here is, for example, a CD (Compact Disc), a DVD (Digital Versatile Disc), a CD-R (Recordable) and a DVD-R (Recordable) that allow additional recording of information, and information can be rewritten. CD-RW (ReWritable), DVD-RW (ReWritable), DVD + RW (ReWritable), DVD-RAM (Random Access Memory) and other optical disks, and a semiconductor laser with a shorter emission wavelength of about 405 nm (blue-violet) A high-density recording optical disk capable of high-density recording, a magneto-optical disk, and the like.

  In particular, the following three types of optical discs for reproducing or recording information by the optical disc apparatus 10 can perform high-density recording using a light beam having a protective substrate thickness of 0.1 mm and a wavelength of about 405 nm as recording / reproducing light. The first optical disk 4, the second optical disk 5 such as a DVD using a light beam having a wavelength of about 655 nm as recording / reproducing light with a protective substrate thickness of 0.6 mm, and a protective substrate thickness of 1.2 mm A description will be given assuming that a third optical disk 6 such as a CD using a light beam having a wavelength of about 785 nm as recording / reproducing light is used.

  As shown in FIG. 1, the optical disk apparatus 10 includes a spindle motor 12 as a driving means for rotating the optical disk 11, a motor control circuit 13 for controlling the spindle motor 12, and an optical beam applied to the optical disk 11 rotated by the spindle motor 12. Pickup 1 that detects the return light beam reflected by the optical disk 11, the RF amplifier 15 that amplifies the electrical signal output from the optical pickup 1, and the focus servo signal and tracking servo signal of the objective lens are generated. A servo circuit 16 and a subcode extraction circuit 17 for extracting subcode data are provided.

  The optical disk apparatus 10 is connected to a host device such as a personal computer as a recording system, and has an input terminal 18 to which data to be recorded is input, and an error correction code for the recording data input to the input terminal 18. An error correction encoding circuit 19 that performs the encoding process, a modulation circuit 20 that modulates the data that has been subjected to the error correction encoding process, and a recording processing circuit 21 that performs the recording process on the modulated recording data.

  Further, the optical disc apparatus 10 includes, as a reproduction system, a demodulation circuit 22 that demodulates reproduction data read from the optical disc 11, an error correction decoding circuit 23 that performs error correction decoding processing on the demodulated reproduction data, And an output terminal 24 for outputting data subjected to error correction decoding processing. Furthermore, the optical disc apparatus 10 discriminates the type of the optical disc 11, an operation unit 25 for inputting operation signals to the device, a memory 26 for storing various control data, a control circuit 27 for controlling the overall operation, and the like. A disc type determination unit 29; Furthermore, the optical disk device 10 includes a thread motor 28 that serves as a drive source when the optical pickup 1 is fed in the radial direction of the optical disk 11 mounted on the disk table.

  The spindle motor 12 is provided with a disk table on which the optical disk 11 is mounted on the spindle, and rotates the optical disk 11 mounted on the disk table. The motor control circuit 13 drives and controls the spindle motor 12 so that the optical disk can be rotated by CLV (Constant Linear Velocity). Specifically, the motor control circuit 13 drives and controls the spindle motor 12 so that the rotational speed of the optical disk 11 is constant based on the reference clock from the crystal oscillator and the clock from the PLL circuit. The optical disk 11 may be rotated by control combining CAV (Constant Angular Velocity) or CLV and CAV.

  The optical pickup 1 is an optical pickup having, for example, a three-wavelength compatible optical system that emits a wavelength according to the type of the mounted optical disk 11, and has the above-described different wavelengths for the signal recording surfaces of optical disks with different standards. A light source such as a semiconductor laser that emits a beam, an objective lens having a numerical aperture corresponding to the type of the optical disk 11 that focuses the light beam emitted from the light source, and a light detection that detects a return light beam reflected by the optical disk 11 Equipped with containers. The optical pickup 1 emits a light beam that is laser light from a semiconductor laser. The optical pickup 1 irradiates the optical disk 11 with a light beam at the time of recording / reproduction, detects the returned light beam reflected by the signal recording surface with a photodetector, and performs photoelectric conversion. The objective lens is held by an objective lens driving mechanism such as a biaxial actuator, and is driven and displaced in the focus direction parallel to the optical axis of the objective lens based on the focus servo signal. The objective lens is also based on the tracking servo signal. Is driven and displaced in a tracking direction orthogonal to the optical axis. The configuration of the optical system such as the semiconductor laser, the objective lens, and the photodetector will be described in detail later.

  The RF amplifier 15 generates an RF signal, a focus error signal, and a tracking error signal based on an electrical signal from a photodetector that constitutes the optical pickup 1. For example, the focus error signal is generated by the astigmatism method, and the tracking error signal is generated by the three-beam method or the push-pull method. The RF amplifier 15 outputs an RF signal to the demodulation circuit 22 and outputs a focus error signal and a tracking error signal to the servo circuit 16 during reproduction.

  The servo circuit 16 generates a servo signal for reproducing the optical disc 11. Specifically, the servo circuit 16 generates a focus servo signal based on the focus error signal input from the RF amplifier 15 so that the focus error signal becomes zero, and the tracking input from the RF amplifier 15. Based on the error signal, a tracking servo signal is generated so that the tracking error signal becomes zero. The servo circuit 16 outputs the focus servo signal and the tracking servo signal to the drive circuit of the objective lens drive mechanism that constitutes the optical pickup 1. This drive circuit drives a biaxial actuator based on the focus servo signal, displaces objective lenses 34 and 35 described later in a focus direction parallel to the optical axis of the objective lens, and drives the biaxial actuator based on the tracking servo signal. Then, the objective lens is driven and displaced in the tracking direction orthogonal to the optical axis of the objective lens.

  The optical disc apparatus 10 configured as described above rotates the optical disc 11 by the spindle motor 12 and drives and controls the sled motor 28 in accordance with the control signal from the servo circuit 16 so that the optical pickup 1 can be used as desired on the optical disc 11. By moving to a position corresponding to the recording track, information is recorded on and reproduced from the optical disc 11.

  Next, the above-described optical pickup 1 to which the present invention is applied will be described.

  As shown in FIG. 2, the optical pickup 1 to which the present invention is applied has a first light source unit 31 such as a semiconductor laser that emits a first light beam having a first wavelength, and a wavelength that is greater than the first wavelength. A second light source unit 32 such as a semiconductor laser that emits a second light beam having a long second wavelength, and a semiconductor laser that emits a third light beam having a third wavelength longer than the second wavelength And the first light beam emitted from the first to third light source units 31, 32, 33 is condensed on the signal recording surface of the first optical disc 4. The objective lens 34, the second objective lens 35 for condensing the second and third light beams on the signal recording surfaces of the second optical disc 5 and the third optical disc 6, respectively, and the first to third optical discs. A photodetector that detects the return light beam reflected from the signal recording surface And a light detector 36.

  The optical pickup 1 includes a first dichroic prism 37 serving as an optical path combining unit that combines the optical paths of the light beams having the second and third wavelengths emitted from the second and third light source units 32 and 33. The outgoing light beams of the second and third wavelengths synthesized by the first dichroic prism 37 are reflected and emitted to the objective lens 35 side, and the returning light beam reflected by the optical disk 11, that is, the returning light beam. A polarizing beam splitter 38 as an optical path separating means for separating the optical paths of the first to third wavelength light beams from the optical paths of the second and third wavelength light beams, and the forward path reflected by the polarizing beam splitter 38 The optical paths of the second and third wavelength light beams and the optical path of the first wavelength light beam emitted from the first light source unit 31 are combined and reflected by the optical disc 11. A dichroic polarization beam splitter (hereinafter also referred to as “Dichro PBS”) 39 as optical path combining / separating means for separating the optical path of the light beam having the first to third wavelengths in the return path from the optical path of the light beam having the first wavelength in the return path. And an optical path of an incident light beam having a first wavelength, and an optical path of an incident light beam having a second wavelength, which are provided between the dichroic PBS 39 and the first and second objective lenses 34 and 35. And a second dichroic prism that guides the light beam of the first wavelength to the first objective lens 34 side and guides the light beams of the second and third wavelengths to the second objective lens 35 side. 41, and is provided between the dichroic PBS 39 and the second dichroic prism 41. The divergence angles of the first to third wavelength light beams incident after the optical paths are synthesized by the dichroic PBS 39 are converted into parallel light. Kori And a Tarenzu 42.

  Between the second dichroic prism 41 and the first objective lens 34, a rising mirror 43 that reflects the light beam having the first wavelength transmitted through the second dichroic prism 41, and the light having the first wavelength. A quarter-wave plate (QWP) 44 is provided for converting the polarization state by giving a phase of a quarter wavelength to the beam.

  Between the second dichroic prism 41 and the second objective lens 35, the light beam having the second and third wavelengths reflected by the second dichroic prism 41 is given a phase of ¼ wavelength to be polarized. A quarter wave plate (QWP) 45 for converting the state is provided.

  Further, between the first light source unit 31 and the dichroic PBS 39, in order to obtain a tracking error signal or the like for the light beam of the first wavelength emitted from the first light source unit 31, the 0th order light and ± 1 A first grating 46 is provided that is divided into three beams of next light. Between the second light source unit 32 and the first dichroic prism 37, in order to obtain a tracking error signal or the like for the second wavelength light beam emitted from the second light source unit 32, A second grating 47 is provided that is divided into three beams composed of ± primary light. Between the third light source unit 33 and the first dichroic prism 37, in order to obtain a tracking error signal or the like for the light beam of the third wavelength emitted from the third light source unit 33, A third grating 48 is provided that divides the light into three beams composed of ± primary light.

  The optical pickup 1 also includes a magnification conversion lens 49 that converts the divergence angle of the returned light beam between the polarization beam splitter 38 and the photodetector 36, and a polarization state of the light beam to detect a focus error signal. And a polarization diffraction element 50 that transmits and diffracts at a predetermined ratio.

  The first light source unit 31 includes a first emission unit, and emits a light beam having a first wavelength of about 405 nm from the first emission unit to the first optical disc 4. The second light source unit 32 includes a second emission unit, and emits a light beam having a second wavelength of about 655 nm to the second optical disc 5 from the second emission unit. The third light source unit 33 includes a third emission unit, and emits a light beam having a third wavelength of about 785 nm to the third optical disc 6 from the third emission unit.

  The optical pickup 1 is configured to use the first to third wavelength light beams respectively emitted from the respective emission parts of the first to third light source parts 31, 32, and 33 arranged at different positions. However, the present invention is not limited to this, and the first to third emission units may be arranged in the same light source unit, and two of the first to third emission units may be arranged. The emission unit may be arranged in one light source unit, and the remaining emission units may be arranged in another light source unit.

  Each of the first to third gratings 46, 47, and 48 mainly uses an incident light beam as a zero-order light (hereinafter also referred to as “main beam”) and ± first-order light (hereinafter referred to as “side beam”). The light is divided into a plurality of light beams. By the first to third gratings 46, 47, 48, a tracking error signal can be obtained by three beams composed of the divided main beam and side beam.

  The first dichroic prism 37 is a separation surface 37a on which an optical thin film having a wavelength dependency that reflects a light beam having a second wavelength and transmits a light beam having a third wavelength is formed. And the optical paths of the light beams of the second and third wavelengths emitted from the second and third light source units 32 and 33 are combined and emitted toward the polarization beam splitter 38 by the separation surface 37a.

  The polarization beam splitter 38 transmits the entire light amount of the light beam in the P-polarized state out of the passing light beam, and reflects the polarization dependency so as to reflect the substantially total light amount of the light beam in the S-polarization state. A separation surface 38a on which an optical thin film is formed. The separation surface 38a reflects the light beams of the second and third wavelengths in the forward path and guides them to the dichroic PBS 39, and the first to third wavelengths in the return path And is separated from the optical paths of the light beams having the second and third wavelengths in the forward path and guided to the magnification conversion lens 49.

  Here, the polarization beam splitter 38 is configured to transmit the light beam in the P-polarized state and reflect the light beam in the S-polarized state. However, the present invention is not limited to this. You may comprise so that a light beam may be reflected and the light beam of a S polarization state may be permeate | transmitted.

  The dichroic PBS 39 transmits the light beam having the first wavelength in the P-polarized state and reflects the light beam having the first wavelength in the S-polarized state, and the second and third light beams in any polarization state. It has a separation surface 39a on which an optical thin film having both polarization dependency and wavelength dependency for transmitting a light beam having a wavelength is formed. The dichroic PBS 39 reflects the light beam having the first wavelength on the forward path by the separation surface 39a, transmits the light beams having the second and third wavelengths on the forward path, synthesizes these optical paths, and guides them to the collimator lens 42. At the same time, the light beams having the first to third wavelengths in the return path are transmitted and separated from the optical path of the light beam having the first wavelength in the forward path, and are guided to the polarization beam splitter 38.

  The collimator lens 42 converts the divergence angles of the light beams having the first to third wavelengths whose optical paths are synthesized by the dichroic PBS 39, and emits the substantially parallel light to the second dichroic prism 41 side.

  The second dichroic prism 41 is formed with an optical thin film having a wavelength dependency that reflects the light beams of the second and third wavelengths among the incident light beams and transmits the light beams of the first wavelength. A separation surface 41a, and the separation surface 41a separates the optical paths of the light beams of the second and third wavelengths in the forward path from the optical paths of the light beams of the first wavelength in the forward path; Is guided to the second objective lens 35 through the quarter-wave plate 45, and the first wavelength light beam is raised through the mirror 43 and the quarter-wave plate 44 to the first objective. Guide to lens 34. Further, the second dichroic prism 41 synthesizes the optical path of the second and third wavelength light beams and the optical path of the first wavelength light beam of the return path by the separation surface 41a. The light is emitted to the 42 side.

  The quarter-wave plate 44 gives a quarter-wave phase difference to the incident light beam of the first wavelength that is transmitted through the second dichroic prism 41 and reflected by the rising mirror 43, that is, incident. The forward light beam is converted from linearly polarized light (S-polarized state) to circularly polarized light, and the return light beam reflected by the optical disk is converted from circularly polarized light to linearly polarized light (P-polarized state).

  The quarter wavelength plate 45 gives a phase difference of ¼ wavelength to the incident light beams of the second and third wavelengths after being reflected by the second dichroic prism 41, that is, the incident forward light beam. The linearly polarized light (S-polarized state) is converted to circularly polarized light, and the return light beam reflected by the optical disk is converted from circularly polarized light to linearly polarized light (P-polarized state).

  The first objective lens 34 corresponds to the light beam having the first wavelength and has a numerical aperture of about 0.85. The first objective lens 34 focuses the light beam having the first wavelength on the signal recording surface 4 a with respect to the first optical disk 4.

  A first aperture filter (not shown) is provided on the incident side of the first objective lens 34 as an aperture limiting element that limits the aperture of the light beam incident on the first objective lens 34. In the first aperture filter, the numerical aperture of the light beam having the first wavelength that passes through is set to about 0.85. As this aperture filter, for example, a hologram or the like is used.

  The second objective lens 35 corresponds to the light beams of the second and third wavelengths, and the numerical aperture is 0.6 to 0.65 for the second wavelength. Is set to 0.45 to 0.5. The second objective lens 35 condenses the light beam of the second wavelength on the signal recording surface 5 a with respect to the second optical disk 5, and the light of the third wavelength with respect to the third optical disk 6. The beam is focused on the signal recording surface 6a.

  On the incident side of the second objective lens 35, a second aperture filter (not shown) is provided as an aperture limiting element that limits the aperture of the light beam incident on the second objective lens 35. In the second aperture filter, the numerical aperture of the light beam having the second wavelength passing through is set to about 0.6 to 0.65, and the numerical aperture of the light beam having the third wavelength passing through is set to 0.45 to. 5 As this aperture filter, for example, a hologram or the like is used.

  The first and second objective lenses 34 and 35 are movably supported by an objective lens driving mechanism such as a biaxial actuator. The first and second objective lenses 34 and 35 are moved by the objective lens driving mechanism on the basis of the tracking error signal and the focus error signal detected by the photodetector 36, thereby approaching the optical disc 11. It is moved in the biaxial direction of the separating direction and the radial direction of the optical disk.

  The first and second objective lenses 34 and 35 have a focal length f1 and a numerical aperture NA1 with respect to the first wavelength of the first objective lens 34, and second and third objective lenses 35. Regarding the relationship between the focal lengths f2 and f3 and the numerical apertures NA2 and NA3, the relational expression fn × NAn (n = 1, 2, 3) is substantially constant, that is, the relational expression of each wavelength (fn × NAn). The focal length is determined so that the difference between the values indicated by is within 20%.

  In other words, the beam diameters of the first to third wavelengths of the light beams emitted from the first and second objective lenses 34 and 35 are approximately the same, and the first and second objective lenses 34 are respectively the same. , 35, the effective diameters of the light beams having the first to third wavelengths in the forward path are set to substantially the same size. Such first and second objective lenses 34 and 35 enable the miniaturization of optical components in the optical paths of the respective wavelengths, and the first to third wavelengths of the return path incident on the polarization diffraction element 50 described later. The beam diameters of the light detectors can be made substantially the same, and the size of each light receiving portion of the photodetector 36 that detects the light beam diffracted and transmitted by the polarization diffraction element 50 can be reduced.

  In addition, the optical pickup 1 is configured to include the first objective lens 34 for the first wavelength and the second objective lens 35 for the second and third wavelengths, but is not limited thereto. It may be configured to provide one or a plurality of objective lenses for condensing the light beams of the first to third wavelengths corresponding to the type of the optical disc on the signal recording surface of the corresponding optical disc. A single objective lens corresponding to the first to third wavelengths may be provided.

  The magnification conversion lens 49 combines the optical paths by the second dichroic prism 41, and diverges the light beams of the first to third wavelengths in the return path that are incident through the collimator lens 42, the dichroic PBS 39, and the polarization beam splitter 38. The angle is converted, and this light beam is focused on each light receiving portion of the photodetector 36 via the polarization diffraction element 50 at a predetermined divergence angle (focusing angle).

  As shown in FIG. 3, the polarization diffraction element 50 diffracts the incident light beam having the first to third wavelengths in one direction of the predetermined direction Xr1 corresponding to the radial direction of the optical disk 11. A plurality of diffraction regions 50a and a plurality of second diffraction regions 50b that diffract the light beams having the first to third wavelengths in the other direction opposite to one direction of the predetermined direction Xr1 are alternately formed. Here, the predetermined direction Xr1 corresponding to the radial direction of the optical disk 11 means that the light beam passes on the polarization diffraction element 50 when the spot of the light beam moves on the signal recording surface of the optical disk 11 in the radial direction. The direction in which the region moves and the direction in which the spot of the light beam on the detector described later moves. The first diffractive region 50a and the second diffractive region 50b are formed in, for example, an elongated rectangular shape having a short side in the diffraction direction and a long side in a direction perpendicular to the diffraction direction, that is, in a lattice shape. Formed so that the total area of the first and second diffraction regions 50a and 50b is substantially equal, and the total area of the light beams passing through the respective regions is substantially equal. Yes.

  In the plurality of first diffraction regions 50a, a blazed grating is formed in each region. That is, in the first diffraction region 50a, a plurality of blazed grating grooves formed in the long side direction are formed side by side in the short side direction, and the groove depth of the blazed grating groove and With the blaze angle, as shown in FIG. 4, the second-order diffracted light of the first wavelength light beam is diffracted so as to be collected in front of the fourth light receiving section 54, and the second and third wavelength light beams The first-order diffracted light is diffracted so as to be collected in front of the fourth light receiving unit 54.

  The plurality of second diffraction regions 50b are each formed with a blazed grating inclined in the opposite direction to the blazed shape of the first diffraction region 50a. That is, in the second diffraction region 50b, a plurality of blazed grating grooves formed in the long side direction are formed side by side in the short side direction, and the groove depth of the blazed grating groove and As shown in FIG. 4, the second-order diffracted light of the light beam having the first wavelength is diffracted by the blaze angle so as to be condensed on the back side of the fifth light receiving unit 55, and the light having the second and third wavelengths. The first-order diffracted light of the beam is diffracted so as to be condensed on the back side of the fifth light receiving unit 55. Here, the grating structure of the first and second diffraction regions 50a and 50b is a blazed shape, but a plurality of grating grooves having a plurality of steps in one pitch may be formed. Good.

  The first and second diffraction regions 50a and 50b have different diffraction powers, that is, diffraction angles, depending on their blaze angles. For example, as described above, the first diffraction region 50 a transmits the diffracted light between the polarization diffraction element 50 and the fourth light receiving unit 54, that is, with respect to the polarization diffraction element 50. The second diffraction region 50b diffracts the diffracted light so as to focus on the polarization diffraction element 50 on the rear side of the fifth light receiving portion 55. The polarization diffraction element 50 diffracts the incident return light beam by the first and second diffraction regions 50a and 50b and obtains predetermined light receiving portions 54 and 55 in order to obtain a focus error signal by a spot size method described later. The light is emitted toward

Further, the first and second diffraction regions 50a and 50b of the polarization diffraction element 50 have different diffraction directions as described above, but the diffraction efficiency changes depending on the change in the polarization state of the incident light beam. That is, for example, the first and second diffraction regions 50a and 50b of the polarization diffraction element 50 function as a diffraction grating as described above for a light beam having a predetermined polarization direction, and are orthogonal to the predetermined polarization direction. The light beam in the polarization direction does not function as a diffraction grating and is transmitted. In other words, the polarization diffraction element 50 diffracts a light beam having a predetermined polarization direction component in the incident light beam and transmits a light beam having a polarization direction component orthogonal to the predetermined polarization direction. If the angle between a predetermined polarization direction in which the light beam is diffracted by the polarization diffraction element 50 and the polarization direction of the light beam incident on the polarization diffraction element 50 is θ, the polarization diffraction element 50 Of the light beam incident on the light beam is diffracted at a ratio represented by (cos θ) ² .

  The first and second diffraction regions 50a and 50b have a predetermined polarization state with respect to the first wavelength due to the blazed groove depth described above, that is, a light beam in a polarization state that is diffracted. 70% or more of the second order diffracted light is obtained with respect to the amount of light, and the second and third wavelengths are in a predetermined polarization state, that is, 70% or more of the light beam in the polarization state to be diffracted. Next-order diffracted light is obtained. Here, the above-mentioned ratio with respect to the light quantity of the diffracted polarized light beam is the ratio of the output light quantity to the incident light quantity in the diffracted polarization component. In other words, the first and second diffraction regions 50a and 50b have a diffraction efficiency of the above-mentioned orders of diffracted light of the first to third wavelengths when a light beam is incident in a polarization state that is 100% diffracted. 70% or more.

FIG. 5 shows a change in diffraction efficiency associated with a change in the groove depth of the blaze in the first and second diffraction regions 50a and 50b in which the above-described blaze-shaped grating grooves are formed. In FIG. 5, the horizontal axis indicates the groove depth (nm) converted into the optical path length difference. Further, in FIG. 5, each curve indicates the ratio of the incident light quantity and the outgoing light quantity in the diffracted polarization component, that is, the diffraction efficiency, and the curves L ₁₀ , L ₁₁ , and L ₁₂ each have a wavelength of 405 nm ( The first-order diffracted light beam, the first-order diffracted light beam, and the second-order diffracted light beam are indicated by curves L ₂₀ , L ₂₁ , and L ₂₂ , respectively. The 0th-order diffracted light, 1st-order diffracted light, and 2nd-order diffracted light are shown, and the curves L ₃₀ , L ₃₁ , and L ₃₂ are the 0th-order diffracted light, 1st-order diffracted light, 2 It shows the next diffracted light. As shown in FIG. 5, the polarization diffraction element 50 has the second wavelength of the first wavelength within the range of the groove depth of the blaze formed in the first and second diffraction regions 50a and 50b in the range of about 700 nm to 800 nm. The diffraction efficiency of the folded light and the first-order diffracted light of the second and third wavelengths can be diffracted at 70% or more.

  Since the polarization diffraction element 50 uses a diffracted light of different orders for the first wavelength and the second and third wavelengths, the fourth and fifth light receiving parts 54, 54, which will be described later, for any wavelength. The light can be condensed at approximately the same position of 55. That is, generally, when a light beam having a different wavelength is diffracted by a diffraction element, the diffraction angle is proportional to the wavelength. For example, for a light beam having a short wavelength, the wavelength of the first wavelength The long light beams of the second and third wavelengths are diffracted in the spreading direction, and a difference occurs in the position of the diffracted light at the light receiving portion. Therefore, it is necessary to increase the size of the light receiving portion. On the other hand, in the polarization diffraction element 50, the size of the fourth and fifth light receiving portions 54 and 55 can be reduced because of the configuration using diffracted light of different orders.

  As shown in FIG. 6, the photodetector 36 receives first to third light beams that are split into three beams by the first to third gratings 46, 47, and 48 and transmitted through the polarization diffraction element 50. Of the light beams divided into three beams by the light receiving portions 51, 52, and 53 and the first to third gratings 46, 47, and 48, light beams obtained by diffracting the main beam, which is zero-order light, by the polarization diffraction element 50 are received. And fourth and fifth light-receiving portions 54 and 55.

  The first light receiving unit 51 is a photodetector that receives a light beam that has been transmitted through the polarization diffraction element 50 among a plurality of light beams diffracted by the gratings 46, 47, and 48, and is orthogonal to each other. Each of the light receiving areas A, B, C, and D is divided into approximately four equal parts by a set of dividing lines.

  The second and third light-receiving units 52 and 53 are two side beams that are ± first-order light among the plurality of light beams diffracted by the gratings 46, 47, and 48 and transmitted through the polarization diffraction element 50. A pair of photodetectors that respectively receive the light beams, and each of the light receiving regions E1, F1 and each light receiving region E2 that are substantially divided into two equal parts by a dividing line in a direction orthogonal to the direction Xr2 corresponding to the radial direction of the optical disc 11. , F2. Note that the second and third light receiving portions 52 and 53 are arranged away from the first light receiving portion 51 in one and the other in the direction orthogonal to the direction Xr2 corresponding to the radial direction of the optical disc 11. Yes.

  The fourth light receiving unit 54 is a photo detector that receives the main beam diffracted by the gratings 46, 47, and 48 and the light beam diffracted by the first diffraction region 50 a of the polarization diffraction element 50. Each light receiving region G1, H1, J1 is divided into three by two dividing lines substantially parallel to the direction Xr2 corresponding to the radial direction. The fifth light receiving unit 55 is a photodetector that receives the main beam diffracted by each grating and the light beam diffracted by the second diffraction region 50 b of the polarization diffraction element 50, and corresponds to the radial direction of the optical disk 11. Each light receiving region G2, H2, J2 is divided into three by two dividing lines substantially parallel to the direction Xr2. Note that the fourth and fifth light receiving portions 54 and 55 are spaced from the first light receiving portion 51 in one and the other in the direction Xr2 corresponding to the radial direction of the optical disc 11.

  The photodetector 36 outputs the outputs from the light receiving areas A to D, E1, E2, F1, F2, G1 to J1, G2 to J2 of the first to fifth light receiving parts 51 to 55, respectively, SA, SB, As SC, SD, SE1, SE2, SF1, SF2, SG1, SH1, SJ1, SG2, SH2, and SJ2, it is possible to obtain various signals such as a focus error signal and a tracking error signal together with an information signal.

Specifically, in order to generate the focus error signal by the optical pickup 1, the light beams diffracted by the first and second diffraction regions 50a and 50b are received by the fourth and fifth light receiving units 54 and 55, respectively. Detection is performed using a spot size (SSD) method based on the amount of light beam. The focus error signal FE by this spot size method is obtained by the following equation (1).
FE = (SG1 + SJ1 + SH2) − (SG2 + SJ2 + SH1) (1)

The generation of the tracking error signal by the optical pickup 1 selectively uses a differential phase detection (DPD) method and a differential push-pull (DPP) method. To detect. The tracking error signal TE1 by the DPD method is obtained by the following equation (2), and the tracking error signal TE2 by the DPP method is obtained by the following equation (3). In Expression (2), Phase (A + C) is a phase obtained by adding the phases detected in the light receiving areas A and C, and Phase (B + D) is a phase detected in the light receiving areas B and D. It is the phase that added together. In Equation (3), k is a value determined so as to remove the offset component.
TE1 = Phase (A + C) −Phase (B + D) (2)
TE2 = {(SA + SD)-(SB + SC)}-k {(SE1-SF1) + (SE2-SF2)} (3)

  The optical pickup 1 configured as described above drives the first or second objective lenses 34 and 35 based on the focus error signal and tracking error signal generated by the return light detected by the photodetector 36. Then, focus servo and tracking servo are performed. By driving the first or second objective lens 34, 35, the objective lens is moved to the focal position with respect to the recording surface of the optical disc 11, and the light beam is focused on the recording surface of the optical disc 11. Then, information is recorded on or reproduced from the optical disc 11.

  Next, the optical path of the light beam emitted from the first to third light source parts 31, 32, 33 in the optical pickup 1 will be described with reference to FIG. First, the optical path of the first wavelength light beam emitted to the first optical disc 4 will be described.

  Based on the signal from the disc type discriminating unit 29 that discriminates that the optical disc 11 is the first optical disc 4, the first light source unit 31 emits a light beam having the first wavelength.

  The light beam of the first wavelength emitted from the first light source unit 31 is divided into a plurality of light beams including a main beam and a side beam by the first grating 46, reflected by the dichroic PBS 39, and reflected by the collimator lens 42. The light is substantially parallel light, passes through the second dichroic prism 41, is reflected by the rising mirror 43, is circularly polarized by the ¼ wavelength plate 44, and is reflected by the first objective lens 34 to the first optical disk 4. On the signal recording surface.

  The light beam condensed on the first optical disk 4 is reflected by the signal recording surface, and passes through the quarter wavelength plate 44, the rising mirror 43, the second dichroic prism 41, and the collimator lens 42, and then the dichroic PBS 39. Then, the light is transmitted through the polarization beam splitter 38, the divergence angle is converted by the magnification conversion lens 49, and is incident on the polarization diffraction element 50.

  A part of the main beam of the light beam having the first wavelength incident on the polarization diffraction element 50 is a predetermined ratio according to the polarization state and diffraction efficiency, and the light beam incident on the first diffraction region 50a is the first beam. The light beam diffracted to the fourth light receiving portion 54 side and incident on the second diffraction region 50b is diffracted to the fifth light receiving portion 55 side. In addition, the main beam of the light beam having the first wavelength incident on the polarization diffraction element 50 is transmitted at a predetermined ratio according to the polarization state, and is condensed on the first light receiving unit 51. The Further, the side beam of the light beam having the first wavelength incident on the polarization diffraction element 50 is transmitted at a predetermined ratio according to the polarization state and is condensed on the second and third light receiving parts 52 and 53. The

  Next, the optical path of the light beam having the second wavelength emitted to the second optical disc 5 will be described.

  Based on the signal from the disc type discriminating unit 29 that discriminates that the optical disc 11 is the second optical disc 5, the second light source unit 32 emits a light beam having the second wavelength.

  The light beam of the second wavelength emitted from the second light source unit 32 is divided into a plurality of light beams by the second grating 47, reflected by the first dichroic prism 37, and reflected by the polarization beam splitter 38. Then, the light passes through the dichroic PBS 39, is made substantially parallel light by the collimator lens 42, is reflected by the second dichroic prism 41, is circularly polarized by the quarter wavelength plate 45, and is secondly reflected by the second objective lens 35. The light is focused on the signal recording surface of the optical disc 5.

  The light beam condensed on the second optical disk 5 is reflected by the signal recording surface, and enters the dichroic PBS 39 via the quarter-wave plate 45, the second dichroic prism 41, and the collimator lens 42. Since the optical path after the light beam having the second wavelength in the return path is incident on the dichroic PBS 39 is the same as the light beam having the first wavelength in the return path described above, detailed description thereof is omitted.

  Further, the optical path of the light beam having the third wavelength emitted to the third optical disc 6 is emitted from the third light source unit 33, divided by the third grating 48 into a plurality of light beams, The optical path of the light beam having the second wavelength is the same as that described above except that it passes through the dichroic prism 37 and enters the polarization beam splitter 38, so that detailed description thereof is omitted.

  As described above, the optical pickup 1 appropriately collects the light beams having the first to third wavelengths on the signal recording surfaces of the plurality of types of optical disks 4, 5, and 6, respectively, The information signal can be detected by transmitting a part of the light beam having the wavelength of 3 through the polarization diffraction element 50 and detecting it by the first light receiving unit 51. The optical pickup 1 also receives the diffracted light diffracted by the first and second diffraction regions 50a and 50b of the common polarization diffraction element 50 provided in the optical path of the light beam having the first to third wavelengths on the return path. The light can be received by the common fourth and fifth light receiving portions 54 and 55, respectively, and a focus error signal can be detected using the spot size method. In addition, the optical pickup 1 condenses the light beams having the first to third wavelengths generated by the gratings 46, 47, and 48 on the signal recording surface of the optical disc, and outputs one of the return light beams. The part is transmitted through the polarization diffraction element 50 and received by the common first to third light receiving parts 51, 52 and 53, and the tracking error signal can be detected by the DPD method or the DPP method. As described above, the optical pickup 1 detects servo signals such as a focus error signal and a tracking error signal for a plurality of types of optical disks using a common optical component, thereby realizing good recording and reproduction, and is compatible with three wavelengths. Realize.

  In addition, the optical pickup 1 detects the focus error signal by the spot size method in particular, and the first and second diffraction regions 50a and 50b of the polarization diffraction element 50 have the second-order diffracted light of the light beam of the first wavelength. The diffraction efficiency is 70% or more, and the diffraction efficiency of the first-order diffracted light of the light beams of the second and third wavelengths is 70% or more. With the first wavelength and the second and third wavelengths, By using diffracted light of different orders, the diffracted light of each wavelength of the polarization diffraction element 50 can be condensed at substantially the same position, and the sizes of the light receiving portions 54 and 55 can be reduced. The light beam diffracted by the polarization diffraction element 50 is detected by the common light receiving parts 54 and 55, so that a good focus error signal can be detected and the light receiving parts 54 and 55 can be downsized.

  Therefore, the optical pickup 1 to which the present invention is applied can detect servo signals corresponding to three different wavelengths, and realize miniaturization of optical components, miniaturization of the apparatus, and cost reduction.

  Further, in the optical pickup 1, the beam diameters of the first to third wavelengths of light beams emitted from the first to second objective lenses 34 and 35 are approximately the same, that is, polarization diffraction. Since the beam diameters of the first to third wavelength light beams incident on the element 50 are substantially the same, the fourth and fifth light receiving portions 54 and 55 can be further reduced in size. Further, the first to third light receiving portions 51, 52, and 53 can be miniaturized, and the optical components in the forward and return paths can be miniaturized, thereby reducing the size and cost of the apparatus.

  An optical disc apparatus 10 using an optical pickup to which the present invention is applied includes the optical pickup 1 described above, and detects a good servo signal corresponding to three different wavelengths in a state where optical components and optical paths of the optical pickup are made common. As a result, it is possible to record and / or reproduce information signals with respect to the optical disc, and to further reduce the size of the optical component, the size of the apparatus, and the cost.

1 is a block circuit diagram of an optical disc apparatus using an optical pickup to which the present invention is applied. It is an optical path diagram explaining an optical system of an optical pickup to which the present invention is applied. It is a top view of the polarization | polarized-light diffraction element which comprises the optical pick-up to which this invention is applied. It is a figure explaining the light beam diffracted by the polarization diffraction element which comprises the optical pickup to which this invention is applied, and is a side view of a polarization diffraction element and a photodetector. It is a figure which shows the change of the diffraction efficiency of each diffraction order of the light beam of each wavelength accompanying the change of the groove depth of the polarization | polarized-light diffraction element which comprises the optical pickup to which this invention is applied. It is a top view which shows each light-receiving part of the photodetector which comprises the optical pick-up to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up, 10 Optical disk apparatus, 11 Optical disk, 12 Spindle motor, 27 Control part, 29 Disk type discrimination | determination part, 31 1st light source part, 32 2nd light source part, 33 3rd light source part, 34 1st light source part Objective lens, 35 Second objective lens, 36 Photo detector, 42 Collimator lens, 44, 45 1/4 wavelength plate, 46 First grating, 47 Second grating, 48 Third grating, 50 Polarization diffraction element 50a first diffraction region, 50b second diffraction region, 51 first light receiving portion, 52 second light receiving portion, 53 third light receiving portion, 54 fourth light receiving portion, 55 fifth light receiving portion

Claims (4)

A first emission part for emitting a light beam of a first wavelength;
A second emission part for emitting a light beam having a second wavelength longer than the first wavelength;
A third emitting section for emitting a light beam having a third wavelength longer than the second wavelength;
An objective lens for condensing the light beams of the first to third wavelengths emitted from the first to third emitting portions on the signal recording surface of the optical disc;
A photodetector for detecting a return light beam reflected by the signal recording surface of the optical disc;
The optical path of the return light beam is provided between the first to third emission parts and the objective lens, and is separated from the optical path of the light beam emitted from the first to third emission parts. Optical path separating means for guiding the returning light beam to the photodetector side;
A first diffractive region provided between the photodetector and the optical path separating means, which diffracts a passing light beam in a predetermined direction, and a second diffracting the passing light beam in a predetermined other direction. Polarization diffraction elements formed alternately with the diffraction regions,
The photodetector includes a first light receiving unit that receives the light beam diffracted in the first diffraction region, and a second light receiving unit that receives the light beam diffracted in the second diffraction region. Have
The light beam diffracted by the first diffraction region is collected on the front side of the first light receiving unit, and the light beam diffracted by the second diffraction region is on the rear side of the second light receiving unit. A focus error signal is detected based on the light amount of the light beam collected by the first and second light receiving units,
The polarization diffraction element diffracts the light beam when the incident light beam has a predetermined polarization direction, and when the incident light beam has a polarization direction orthogonal to the predetermined polarization direction. Transmits the light beam,
In the first and second diffraction regions, the diffraction efficiency of the second-order diffracted light of the light beam having the first wavelength is 70% or more with respect to the light amount of the light beam in the polarization state to be diffracted. And an optical pickup in which the diffraction efficiency of the first-order diffracted light of the light beam of the third wavelength is 70% or more.   2. The optical pickup according to claim 1, wherein blazed grating grooves are formed in the first and second diffraction regions, respectively.   2. The optical pickup according to claim 1, wherein grating grooves each having a step shape are continuously formed in the first and second diffraction regions. In an optical disc apparatus comprising an optical pickup for recording and / or reproducing information with respect to an optical disc, and a disc rotation driving means for rotating the optical disc,
The optical pickup includes a first emission unit that emits a light beam having a first wavelength;
A second emission part for emitting a light beam having a second wavelength longer than the first wavelength;
A third emitting section for emitting a light beam having a third wavelength longer than the second wavelength;
An objective lens for condensing the light beams of the first to third wavelengths emitted from the first to third emitting portions on the signal recording surface of the optical disc;
A photodetector for detecting a return light beam reflected by the signal recording surface of the optical disc;
The optical path of the return light beam is provided between the first to third emission parts and the objective lens, and is separated from the optical path of the light beam emitted from the first to third emission parts. Optical path separating means for guiding the returning light beam to the photodetector side;
A first diffractive region provided between the photodetector and the optical path separating means, which diffracts a passing light beam in a predetermined direction, and a second diffracting the passing light beam in a predetermined other direction. Polarization diffraction elements formed alternately with the diffraction regions,
The photodetector includes a first light receiving unit that receives the light beam diffracted in the first diffraction region, and a second light receiving unit that receives the light beam diffracted in the second diffraction region. Have
The light beam diffracted by the first diffraction region is collected on the front side of the first light receiving unit, and the light beam diffracted by the second diffraction region is on the rear side of the second light receiving unit. A focus error signal is detected based on the light amount of the light beam collected by the first and second light receiving units,
The polarization diffraction element diffracts the light beam when the incident light beam has a predetermined polarization direction, and when the incident light beam has a polarization direction orthogonal to the predetermined polarization direction. Transmits the light beam,
In the first and second diffraction regions, the diffraction efficiency of the second-order diffracted light of the light beam having the first wavelength is 70% or more with respect to the light amount of the light beam in the polarization state to be diffracted. And an optical disc apparatus in which the diffraction efficiency of the first-order diffracted light of the light beam of the third wavelength is 70% or more.

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